Data storage in large organizations is of fundamental importance, both for data reliability and for the ability to recover data in the event of any hardware failure. Storage area network (SAN) is an architecture used when very large amounts of data must be stored in a reliable and secure manner. This technology allows networks to be created that support the attachment of remote computer storage devices such as disk arrays to servers in such a way that, to the operating system, the devices appear as locally attached. It is common in such networks to include a large amount of redundancy, both in the data storage and in the hardware connections among the individual components.
Various methods exist for creating data redundancy. For example, a function such as the flashcopy function enables an administrator to make point-in-time, full volume copies of data, with the copies immediately available for read or write access. The flashcopy can be used with standard backup tools that are available to create backup copies on tape. Flashcopy creates a point-in-time copy of a source volume on a target volume.
When a flashcopy operation is initiated, a relationship is created between a source volume and a target volume. This relationship involves a “mapping” of the source volume and the target volume. This mapping allows a point-in-time copy of the source volume to be copied to the associated target volume. The relationship exists between this volume pair from the time that the flashcopy operation is initiated until the time that the relationship is ended.
When data is physically copied, a background process copies tracks from the source volume to the target volume. The amount of time necessary to complete the background copy depends on various criteria, including the amount of data being copied, the number of background copy processes that are occurring, and any other activities that are presently occurring.
In storage, the user can create a flashcopy that creates a point-in-time backup of some storage disks. If the user subsequently has a storage problem, the user can use the flashcopy to restore the saved version of the data. More specifically, the direction of the flashcopy relationship can be reversed such that the volume that was previously defined as the target becomes the source for the volume that was previously defined as the source (which is now the target). In such case, modified data is copied to the volume previously defined as the source.
An administrator can reverse a flashcopy relationship if the administrator wishes to restore a source volume (volume A) to a point in time before the flashcopy operation was originally performed. In effect, the administrator is reversing the flashcopy operation so that it appears as though no flashcopy operation ever happened. The background copy process of a flashcopy operation must complete before it is possible to reverse volume A as the source and volume B as the target.
There will be certain circumstances when it is desired to reverse an original flashcopy relationship. For example, a flashcopy relationship may be created between source volume A and target volume B, and then data loss occurs on source volume A. In such case, it is possible to reverse the flashcopy relationship so that volume B is copied to volume A.
Backup processes, such as flashcopy, are commonly configured to occur automatically in relation to a storage volume such as a disk. Such backup occurs periodically, for example every 24 hours. It is also known to link the backup processes of multiple storage devices together in a storage device backup consistency group, which details multiple storage devices and their respective backup locations. A storage backup consistency group simplifies the backup process and also creates a single location to store the details of the backup for multiple storage devices, which in turn can be handled easily for administration purposes. However, a drawback of such a system is that if the underlying hardware is changed (e.g., through the addition of another storage device), the backup procedure for the new storage device may not be linked to an already existing storage device backup consistency group.